Optical Magnetic Properties Of Rare Earth Doped Layered MoS₂ And SnS₂

In recent years,layered metal dichalcogenides（LMDs）have gained extensive attention in fundamental research due to their unique electronic,mechanical and optical properties.And LMDs have practical applications in different fields,such as photovoltaics,superconductors,lithium-ion batteries,supercapacitors and spintronics.MoS₂ and SnS₂ are typical LMDs,but the non-magnetic nature limits applications in many fields.Doping is an effective method to change the intrinsic properties of non-magnetic semiconductor materials.The rare earth elements are ideal dopants due to the inner f orbit,which is not easily affected by the crystal field.Doping of RE elements can change the optical,magnetic and other properties of the host material by randomly replacing the cations into the crystal lattice.In this work,based on MoS₂and SnS₂,a series of LMDs with magnetic characteristics were prepared by doping different concentrations of RE elements.The influence of doping concentration on the optical and magnetic properties of the as-synthesized samples was studied.The electronic structure and magnetic origin of each system were further researched by the first principles calculations.The main contents of this article are as follows:1.The ferromagnetic MoS₂:Dy nanosheets have been obtained by doping various concentration of Dy³⁺dopant.Dy³⁺ions incorporate into MoS₂ host lattice by replacing Mo⁴⁺ions to distort the crystal lattice.The as-synthesized Dy doped MoS₂nanosheets are room-temperature ferromagnetic and the saturation magnetization reaches a maximum value of 0.023 emu/g.The ferromagnetism originates from the interaction among the S 3p orbital,Mo 4d orbital and Dy 5d orbital.2.The MoS₂:Ho nanocrystals with different doping concentrations have been synthesized,and the as-obtained samples show the room-temperature ferromagnetism.The saturation magnetization reaches a maximum value of 0.055 emu/g.The distortion of the lattice and the increased defect levels are caused by the substitution Ho³⁺ions,which can affect the maximum absorption wavelength.The ferromagnetism is derived from the strong hybridization of the Ho 4f orbital with the Mo atom nearest to the Ho atom 4d orbital and the S 3p orbital.3.The SnS₂:Ce nanoparticles with various doping concentrations have been synthesized.The samples have strong absorption in the range of 200 nm–700 nm,and the RE Ce³⁺ion doping can change the absorption edge position of the samples and enhance the surface defect state of the samples.Furthermore,the synthesized samples are room-temperature ferromagnetic,and the saturation magnetization reaches a maximum value of 0.081 emu/g.The ferromagnetism mainly comes from the d–f exchange interaction of doped Ce ions.4.The SnS₂:Ho nanosheets with different doping concentration have been fabricated.Doping affects the optical band gap and increases defect concentration of the nanosheets.The as-prepared samples are room temperature ferromagnetic,and its saturation magnetization reaches a maximum value of 0.072 emu/g.The ferromagnetism originates from not only the Sn vacancies but also the Ho substitution in the sample.